The present invention relates to disk data storage devices and more particularly to a system wherein multiple disk spindle assemblies are synchronously rotated with respect to one another to have the indices coincide or maintain a predetermined or programmable out-of-phase relationship.
A conventional disk drive ham a disk carrying spindle assembly that is closely speed regulated to maintain the rotational velocity of the disk media. The spindle motor is accelerated or decelerated in accordance with the phase error generated by the difference between a reference signal and rotational disk position feedback from the disk carrying spindle.
To obtain enhanced performance drives are commonly rotated j n synchronism with one another. Typical of such synchronized drives are multiple drives used in a synchronous array system where data is interleaved to enhance the data rate and performance or in systems where the latency delay is reduced by having two mirrored drives synchronized to rotate 180 degrees out of phase. The synchronism is best accomplished by using a single source of pulses to define the synchronizing index mark, If data is used from the disk surface of one drive within the system, an event that requires recovery by the primary drive also necessitates secondary recovery by the other drives prior to reestablishing the synchronized operation thereby compromising system performance. Another solution is to use an external oscillator to provide a common source of pulses that is decoded to produce a single precision index reference. Such s system is shown and described in U.S. Pat. No. 4,918,544 which uses a single crystal oscillator to supply the synchronization control circuits respectively associated with the drives within the system. Although this approach affords a control source that could avoid secondary recovery procedures when any drive in the system loses synchronized operation, it would require a separate clocking apparatus or two types of drive apparatus so that a system would use one unit including the clocking apparatus and other units without such structure.